DESCRIPTION The role of DNA methylation in the protection of the genome from foreign genetic material is well documented and understood in prokaryotic systems. The role of DNA methylation in the expansion of the coding potential of the gnome and in the control of differential and development has only recently been appreciated. Detailed investigation of the role of methyltransferases in differentiation and development is experimentally challenging for a number of reasons. Traditional developmental biology model systems such as Drosophila yeast and C. elegans lack methyltransferases altogether. Mammalian methyltransferases are difficult to study in vivo because of the structural, genetic and regulatory complexity of the mammalian cell, and because the enzymes are not essential for proliferation. This proposal is focused on the elaboration of a detailed kinetic model of the cell cycle regulated adenine DNA methyltransferase (CcrM) from Caulobacter crescentus. C. crecentus is a dimorphic, gram negative bacteria for which differentiation is an obligatory step of the cell cycle. As such, these bacteria constitute an elegant model of the genetic and biochemical determinants of differentiation and development. The methyltransferase is an important component of the developmental machinery of C. crescentus and is essential for the viability of these organisms. It also exhibits considerable functional similarity to mammalian methyltransferases in that lacks a cognitive restriction endonuclease, it prefers hemimethylated DNA substrates and it methylates DNA processively. Detailed studies of the kinetic mechanism of CcrM should facilitate understanding of its role in C. crescentus differentiation and provide a paradigm for the role of DNA methylation in development.